Battery products have a general disadvantage compared to corded AC products since battery capacity is expensive and heavy. Furthermore, battery voltage is reduced during a discharge cycle of a battery. In a battery powered vacuum cleaner including an electric motor, a decrease of battery power during the discharge cycle of the battery will result in a decrease of the suction power of the vacuum cleaner during the discharge cycle of the battery. Generally, the maximum inlet power of a fan unit of a vacuum cleaner powered by battery will decrease with half or more during the discharge cycle of the battery. Also, ageing of the battery will impact the power output such that the initial and highest power available can be reduced with more than a third.
In order to limit the effect of battery voltage reduction over a discharge cycle, feedback control has been provided in prior art battery powered vacuum cleaners. In such prior art vacuum cleaner control, feedback of the voltage over a battery of the vacuum cleaner is used, and the voltage provided over the electric motor is controlled towards a target voltage. This will compensate for the battery voltage reduction during the discharge cycle of the battery and hence, such prior art battery powered vacuum cleaners are less affected by the decreasing battery voltage over the discharge cycle of the battery.
A problem with the prior art methods of controlling battery powered electric motors in vacuum cleaners is that the motor power and hence the suction power has to be limited in order to limit the battery capacity required, as batteries with high capacity are expensive and heavy. In some conditions, e.g. when an inlet of the vacuum cleaner is partially blocked, a dust container of the vacuum cleaner is filled or when a filter of the vacuum cleaner is clogged etc, the suction power of prior art battery powered vacuum cleaners may be less than sufficient.
For corded AC powered vacuum cleaners, voltage reduction over time is not an issue in the same way as for battery powered vacuum cleaners. For such prior art corded AC powered vacuum cleaners the suction power is allowed to vary but at a level which is sufficient for all or at least most conditions. In conditions where the airflow is reduced, the suction power will be reduced. However, these prior art corded AC vacuum cleaners are designed such that the suction power will be sufficient also for conditions with a considerable reduction of airflow. A problem with such prior art corded AC vacuum cleaners is that the overall energy consumption is high.